package util;
import java.io.IOException;
import java.io.OutputStream;

public class LZWEncoder {
	private static final int EOF = -1;

	 private int imgW, imgH;
	 private byte[] pixAry;
	 private int initCodeSize;
	 private int remaining;
	 private int curPixel;

	 // GIFCOMPR.C       - GIF Image compression routines
	 //
	 // Lempel-Ziv compression based on 'compress'.  GIF modifications by
	 // David Rowley (mgardi@watdcsu.waterloo.edu)

	 // General DEFINEs

	 static final int BITS = 12;

	 static final int HSIZE = 5003; // 80% occupancy

	 // GIF Image compression - modified 'compress'
	 //
	 // Based on: compress.c - File compression ala IEEE Computer, June 1984.
	 //
	 // By Authors:  Spencer W. Thomas      (decvax!harpo!utah-cs!utah-gr!thomas)
	 //              Jim McKie              (decvax!mcvax!jim)
	 //              Steve Davies           (decvax!vax135!petsd!peora!srd)
	 //              Ken Turkowski          (decvax!decwrl!turtlevax!ken)
	 //              James A. Woods         (decvax!ihnp4!ames!jaw)
	 //              Joe Orost              (decvax!vax135!petsd!joe)

	 int n_bits; // number of bits/code
	 int maxbits = BITS; // user settable max # bits/code
	 int maxcode; // maximum code, given n_bits
	 int maxmaxcode = 1 << BITS; // should NEVER generate this code

	 int[] htab = new int[HSIZE];
	 int[] codetab = new int[HSIZE];

	 int hsize = HSIZE; // for dynamic table sizing

	 int free_ent = 0; // first unused entry

	 // block compression parameters -- after all codes are used up,
	 // and compression rate changes, start over.
	 boolean clear_flg = false;

	 // Algorithm:  use open addressing double hashing (no chaining) on the
	 // prefix code / next character combination.  We do a variant of Knuth's
	 // algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
	 // secondary probe.  Here, the modular division first probe is gives way
	 // to a faster exclusive-or manipulation.  Also do block compression with
	 // an adaptive reset, whereby the code table is cleared when the compression
	 // ratio decreases, but after the table fills.  The variable-length output
	 // codes are re-sized at this point, and a special CLEAR code is generated
	 // for the decompressor.  Late addition:  construct the table according to
	 // file size for noticeable speed improvement on small files.  Please direct
	 // questions about this implementation to ames!jaw.

	 int g_init_bits;

	 int ClearCode;
	 int EOFCode;

	 // output
	 //
	 // Output the given code.
	 // Inputs:
	 //      code:   A n_bits-bit integer.  If == -1, then EOF.  This assumes
	 //              that n_bits =< wordsize - 1.
	 // Outputs:
	 //      Outputs code to the file.
	 // Assumptions:
	 //      Chars are 8 bits long.
	 // Algorithm:
	 //      Maintain a BITS character long buffer (so that 8 codes will
	 // fit in it exactly).  Use the VAX insv instruction to insert each
	 // code in turn.  When the buffer fills up empty it and start over.

	 int cur_accum = 0;
	 int cur_bits = 0;

	 int masks[] =
	  {
	   0x0000,
	   0x0001,
	   0x0003,
	   0x0007,
	   0x000F,
	   0x001F,
	   0x003F,
	   0x007F,
	   0x00FF,
	   0x01FF,
	   0x03FF,
	   0x07FF,
	   0x0FFF,
	   0x1FFF,
	   0x3FFF,
	   0x7FFF,
	   0xFFFF };

	 // Number of characters so far in this 'packet'
	 int a_count;

	 // Define the storage for the packet accumulator
	 byte[] accum = new byte[256];

	 //----------------------------------------------------------------------------
	 LZWEncoder(int width, int height, byte[] pixels, int color_depth) {
	  imgW = width;
	  imgH = height;
	  pixAry = pixels;
	  initCodeSize = Math.max(2, color_depth);
	 }
	 
	 // Add a character to the end of the current packet, and if it is 254
	 // characters, flush the packet to disk.
	 void char_out(byte c, OutputStream outs) throws IOException {
	  accum[a_count++] = c;
	  if (a_count >= 254)
	   flush_char(outs);
	 }
	 
	 // Clear out the hash table

	 // table clear for block compress
	 void cl_block(OutputStream outs) throws IOException {
	  cl_hash(hsize);
	  free_ent = ClearCode + 2;
	  clear_flg = true;

	  output(ClearCode, outs);
	 }
	 
	 // reset code table
	 void cl_hash(int hsize) {
	  for (int i = 0; i < hsize; ++i)
	   htab[i] = -1;
	 }
	 
	 void compress(int init_bits, OutputStream outs) throws IOException {
	  int fcode;
	  int i /* = 0 */;
	  int c;
	  int ent;
	  int disp;
	  int hsize_reg;
	  int hshift;

	  // Set up the globals:  g_init_bits - initial number of bits
	  g_init_bits = init_bits;

	  // Set up the necessary values
	  clear_flg = false;
	  n_bits = g_init_bits;
	  maxcode = MAXCODE(n_bits);

	  ClearCode = 1 << (init_bits - 1);
	  EOFCode = ClearCode + 1;
	  free_ent = ClearCode + 2;

	  a_count = 0; // clear packet

	  ent = nextPixel();

	  hshift = 0;
	  for (fcode = hsize; fcode < 65536; fcode *= 2)
	   ++hshift;
	  hshift = 8 - hshift; // set hash code range bound

	  hsize_reg = hsize;
	  cl_hash(hsize_reg); // clear hash table

	  output(ClearCode, outs);

	  outer_loop : while ((c = nextPixel()) != EOF) {
	   fcode = (c << maxbits) + ent;
	   i = (c << hshift) ^ ent; // xor hashing

	   if (htab[i] == fcode) {
	    ent = codetab[i];
	    continue;
	   } else if (htab[i] >= 0) // non-empty slot
	    {
	    disp = hsize_reg - i; // secondary hash (after G. Knott)
	    if (i == 0)
	     disp = 1;
	    do {
	     if ((i -= disp) < 0)
	      i += hsize_reg;

	     if (htab[i] == fcode) {
	      ent = codetab[i];
	      continue outer_loop;
	     }
	    } while (htab[i] >= 0);
	   }
	   output(ent, outs);
	   ent = c;
	   if (free_ent < maxmaxcode) {
	    codetab[i] = free_ent++; // code -> hashtable
	    htab[i] = fcode;
	   } else
	    cl_block(outs);
	  }
	  // Put out the final code.
	  output(ent, outs);
	  output(EOFCode, outs);
	 }
	 
	 //----------------------------------------------------------------------------
	 void encode(OutputStream os) throws IOException {
	  os.write(initCodeSize); // write "initial code size" byte

	  remaining = imgW * imgH; // reset navigation variables
	  curPixel = 0;

	  compress(initCodeSize + 1, os); // compress and write the pixel data

	  os.write(0); // write block terminator
	 }
	 
	 // Flush the packet to disk, and reset the accumulator
	 void flush_char(OutputStream outs) throws IOException {
	  if (a_count > 0) {
	   outs.write(a_count);
	   outs.write(accum, 0, a_count);
	   a_count = 0;
	  }
	 }
	 
	 final int MAXCODE(int n_bits) {
	  return (1 << n_bits) - 1;
	 }
	 
	 //----------------------------------------------------------------------------
	 // Return the next pixel from the image
	 //----------------------------------------------------------------------------
	 private int nextPixel() {
	  if (remaining == 0)
	   return EOF;

	  --remaining;

	  byte pix = pixAry[curPixel++];

	  return pix & 0xff;
	 }
	 
	 void output(int code, OutputStream outs) throws IOException {
	  cur_accum &= masks[cur_bits];

	  if (cur_bits > 0)
	   cur_accum |= (code << cur_bits);
	  else
	   cur_accum = code;

	  cur_bits += n_bits;

	  while (cur_bits >= 8) {
	   char_out((byte) (cur_accum & 0xff), outs);
	   cur_accum >>= 8;
	   cur_bits -= 8;
	  }

	  // If the next entry is going to be too big for the code size,
	  // then increase it, if possible.
	  if (free_ent > maxcode || clear_flg) {
	   if (clear_flg) {
	    maxcode = MAXCODE(n_bits = g_init_bits);
	    clear_flg = false;
	   } else {
	    ++n_bits;
	    if (n_bits == maxbits)
	     maxcode = maxmaxcode;
	    else
	     maxcode = MAXCODE(n_bits);
	   }
	  }

	  if (code == EOFCode) {
	   // At EOF, write the rest of the buffer.
	   while (cur_bits > 0) {
	    char_out((byte) (cur_accum & 0xff), outs);
	    cur_accum >>= 8;
	    cur_bits -= 8;
	   }

	   flush_char(outs);
	  }
	 }


}
